Which of the following statements is the first step in the synthesis and secretion of T3 and T4?
Synthesis of thyroglobulin by the follicular cells
Oxidation of iodide by the follicular cells
Coupling of T1 and T2
lodide trapping by the follicular cells
The Correct Answer is D
a) Synthesis of thyroglobulin by the follicular cells: This occurs after iodide has been trapped and transported into the follicular lumen.
b) Oxidation of iodide by the follicular cells: This is a later step; iodide must first be trapped before it can be oxidized into iodine.
c) Coupling of T1 and T2: This is one of the final steps in T₃/T₄ synthesis where iodinated tyrosines are joined.
d) lodide trapping by the follicular cells
Iodide trapping is the first step, where follicular cells actively transport iodide from the bloodstream into the thyroid follicle using sodium-iodide symporters.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A,C,B,E,D
No explanation
Correct Answer is A
Explanation
a) Hormonal: This refers to the stimulation of one endocrine gland by hormones released from another gland. GnRH from the hypothalamus stimulates the anterior pituitary to release LH/FSH, which then stimulate the ovaries to secrete estrogen. Thus, this is hormonal control.
b) Neural: Neural stimulation involves direct innervation (e.g., adrenal medulla stimulated by the sympathetic nervous system), which does not apply here.
c) Negative Feedback: This refers to a regulatory mechanism, not the initial cause of estrogen secretion. Estrogen can negatively feedback on GnRH, but that’s not the mechanism being asked.
d) Humoral: Humoral stimuli refer to changes in blood levels of ions or nutrients (e.g., calcium regulating PTH), not hormones.
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